Perception of ELF electromagnetic fields: excitation thresholds and inter-individual variability

Area of Science:

• Electrophysiology
• Human Electrical Safety
• Bioelectromagnetics

Background:

• Current guidelines for electromagnetic field exposure rely on basic limits for intracorporal electric current densities to prevent nerve cell stimulation.
• These limits were established using experimental data extrapolated to the general population, with limited consideration for inter-individual variability in cellular excitability.
• Previous studies on electric current perception thresholds used small sample sizes, leading to inconsistent results and an underestimation of variability.

Purpose of the Study:

• To assess the variability of cellular excitability by measuring electric current perception thresholds in a large and diverse population.
• To compare the sensitivity of men, women, children, and older adults to electric currents.
• To critically review existing safety limits for touch currents in light of new findings on inter-individual variability.

Main Methods:

• Conducted extensive measurements of 50 Hz electric current perception thresholds on 1,071 individuals across various age groups and genders.
• Applied electric currents directly to the lower forearms using a pair of electrodes.
• Utilized numerical simulations to calculate intracorporal electric current densities corresponding to the applied currents.

Main Results:

• Electric current perception thresholds exhibited a log-normal distribution with inter-individual variability spanning two orders of magnitude, significantly higher than previously assumed.
• Women demonstrated significantly higher sensitivity than men, with perception thresholds being substantially lower.
• Children were found to be considerably more sensitive than men and similar to women, with perception thresholds decreasing with age from adult men to boys.

Conclusions:

• Existing safety limits for touch currents require critical review due to the substantial inter-individual variability in electric current perception.
• The findings suggest that current basic limits for intracorporal electric current densities, as recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP), are conservative for preventing cellular excitation.
• Further research is needed to refine safety guidelines that account for the observed variations in human sensitivity to electric fields.